Short-circuit detection probes are used for a variety of applications involving position indication. For example, operations involving cutting, punching or drilling sheet material may require continuous inspection of the material's exact position. The material, preferably in sheet form, may be aligned for the operation with the help of any one or more sensing devices that create a short circuit when alignment is sensed. The short-circuit detection probe then detects the short circuit and may transmit the indication to a controller, according to the specific application. Any change in the proper alignment will be thus sensed and may similarly be reported for a possible correction operation.
Processes that are typically prone to movement of the material are those involving force. For example, a cutting or drilling operation may cause vibrations that will move the material, therefore requiring strong attachment of the material to a base prior to performing the operation. A problem may arise when the attachment, using a certain amount of force, causes a slight movement of the material.
The alignment sensor may be an electrical sensor, suitable for conductive metal substrates, or an optical sensor, such as described for example in Published U.S. patent application Ser. No. 2003/0209680 to the same assignee, having electrical connections.
In CTP devices, such as Lotem 800 available from Creo Inc., Canada, a printing plate blank is mounted on the surface of an external drum for imaging. In order for the plate to be correctly registered on the drum, it is known to use registration pins, mounted on the drum. When the plate is mounted on the drum, its front edge is moved towards the registration pins. When contact is established between the plate's front edge and at least two registration pins, a clamping mechanism is actuated to clamp the front edge of the plate to the drum. The plate is then further wound around the drum and its tail edge also clamped by a rear set of clamps.
Various mechanisms are known for detecting contact between the plate's front end and the registration pins. A special concern is to maintain the contact, once established, throughout the operation of clamping the plate's front-edge to the drum and report any shift to enable correction measures.